NORTH COUNTY  The eastern portion of San Elijo Lagoon offers a less-traveled trail that winds through forests of eucalyptus and a few Torrey pines before it emerges into the coastal sage scrub for glimpses of the namesake lagoon.

This lagoon is also an estuary. It’s fed by two freshwater streams, La Orilla Creek and Escondido Creek, that mix with seawater on their way to the Pacific Ocean. It’s also one of only 16 coastal wetlands remaining in San Diego. Some 90 percent of coastal wetlands in Southern California have been destroyed by development since 1850, so the ones remaining are increasingly important to our region’s biodiversity.

San Elijo Lagoon

Trailhead: For La Orilla trail head, from Interstate 5, exit at Lomas Santa Fe, heading east. Turn left onto Highland Road at the four-way stop, then left onto El Camino Real. Look for the small parking area on the west side of the road, just before El Camino Real makes a sharp 90-degree bend for a brief continuation on La Orilla Road.

Distance: About 3 miles round-trip; allow at least 1.5 hours.

Difficulty: Flat, easy.

Coastal wetlands serve as breeding, resting and nesting grounds for birds, and as hatcheries and feeding grounds for fish. Nearly 300 species of birds either live here or visit during their long seasonal migrations. Some 20 species of fish live in the lagoon, and 26 species of mammals live on the shore.

San Elijo Lagoon began to experience the effects of development more than 100 years ago, when the first railroad was built across the estuary’s mouth in 1882, when the earliest version of Pacific Coast Highway — a wood plank road — was built in 1891 (and paved in 1932), and when Interstate 5 was constructed over it in 1965.

To help protect this coastal wetland, the county and the California Department of Fish and Game periodically open the lagoon mouth by dredging, so the freshwater and seawater can mingle as they would naturally.

I began my hike by first visiting the lagoon’s visitor’s center at its western end, between Pacific Coast Highway and I-5. The center, opened in January 2009, offers informative displays and photographs of the wildlife and habitats found here, as well as some of the area’s history. Pick up free brochures that cover each section of the San Elijo Lagoon Ecological Reserve.

The reserve covers nearly 1,000 acres and has about 7.5 miles of hiking and equestrian trails.

While the western section is more popular and offers more waterscapes and their accompanying waterfowl, the eastern end passes through more kinds of habitat and offers a serene wander through this rich resource.

I started at the La Orilla trailhead at the eastern edge of the lagoon in Rancho Santa Fe, and saw hawks soaring above, great egrets and American coots in the water, and a few cottontail rabbits on the trail.

The first part of the trail passes through riparian woodland, which features willow, sycamore and cottonwood trees. You’ll also see lots of wild grape vines. But non-native eucalyptus have invaded, competing with native plants for water. Their leaves also shed certain chemicals that inhibit the growth of other plants. When these eucalyptus trees die or are removed, the nonprofit citizens’ land trust group, San Elijo Lagoon Conservancy, plants native trees to restore the riparian habitat.

The next habitat is the marsh, where cattails and reeds dominate along the edges of the lagoon’s creeks and ponds. Mule deer graze here along the creek banks.

Chaparral is the next habitat where scrub oak is abundant and where I spotted several bright blue western scrub jays.

The fourth habitat along this trail is coastal sage scrub where low-growing shrubs like sage and buckwheat are plentiful. This time of year the bright red berries of toyon prove why they’re often called Christmas berry.

The trail continues through a powerline easement, where a handful of large Torrey pines stand. Their long needles are five to a bundle.

The La Orilla trail is 3.5 miles from its eastern trail head to the western end of the lagoon’s trail system. But I turned around at the flood control dike just before I-5, which covers about 1.5 miles one-way.

Don’t miss the unmarked, short loop spur on the northern side of the trail that takes you to Tern Point. You can’t miss it — it’s the only spur trail on the northern side.